Sorry, I stand corrected. You guys are correct. Ten years at most.
Okay, then amend all of my previous statements: the framers of the 22nd Amendment intended a 10-year limit.
This, incidentally, weakens the notion that someone who has served 2 terms already has necessarily "reached the limit" according to the intent of the framers of the 22nd Amendment.
That would make it more likely that the USSC would fail to find such a candidate for Vice-President constitutionally ineligible.